Medical nebulizers that nebulize a fluid into an aerosol for inhalation by a patient are well-known devices commonly used for the treatment of certain conditions and diseases. Nebulizers have applications for conscious, spontaneously breathing patients and for controlled, ventilated patients. As used in this specification, the term “patient” includes, without limitation, humans and animals.
In nebulizers, a diverter is primarily used to direct a gas across a liquid channel to create a venturi effect causing the liquid to be entrained into the gas stream. The term “diverter”, as used in this specification, includes, without limitation, any baffle or impinger. As a result of the nebulization process described above, the fluid is transformed into an aerosol, that is, the fluid is caused to form small particles that are suspended in the air and that have a particle size in a range suitable for the intended therapy. A common therapy is inhalation therapy, whereby a patient inhales a medicated aerosol to treat an ailment, such as asthma.
Important considerations in the design of a nebulizer are the timing and dosage regulation of the aerosolized fluid. In some nebulizer designs, a continuous stream of pressurized gas entrains the fluid against the diverter to constantly generate an aerosol until the fluid in a reservoir is depleted. Continuous nebulization may result in a waste of aerosol, such as to the atmosphere, during a patient's exhalation or during a delay between inhalation and exhalation. The amount of wasted aerosol may be difficult to quantify and some of the aerosol may be lost to condensation on the nebulizer or mouthpiece, or to evaporation, during periods of non-inhalation. Nebulizers implementing a timed or non-continuous nebulization may adversely affect particle size and density as the nebulization is turned on and off.
Effective and economical nebulizer therapy includes the ability to quickly generate an aerosol within a desired particle size range. An effective nebulizer preferably provides these features synchronously with the inhalation of the patient. In order to actuate a mechanical nebulizer, a patient's inhalation effort must overcome certain variables. Depending on the structural configuration of the nebulizer, these variables may include one or more of the following: the volumetric flow rate of the flowing gas; air leaks in the device; the force exerted by the flowing gas on a moveable diverter; and the friction between moveable parts. The greater the flow rate, air leaks and friction, the greater the inhalation effort required in order to actuate the device. It is desirable that a nebulizer has adequate sensitivity to quickly respond to an inhalation while not adversely restricting the patient's inhalation.
Most nebulizer designs have difficulty delivering all of the medication that is placed in the nebulizer to the patient. The inefficiency in delivering the medication may stem from some of the medication sticking to the chamber walls of the nebulizer, structural issues in the nebulizer that prevent medication from reaching the desired destination, and other reasons. Failure to use all of the medication adds to the cost of aerosol delivery and can create uncertainty concerning the actual dosage of medication delivered to a patient. Accordingly, it is also desirable to have a nebulizer that is effective for efficiently delivering measured amounts of medication to a patient.